Wind is a powerful renewable energy source that civilizations have harnessed to varying degrees for several thousand years. Historians accredit ancient Mesopotamia and Egypt as giving rise to sail-based propulsion systems for boats, while most accounts accredit ancient Persia as having developed and implemented windmills in 500 to 900 AD. In around 1390, the Dutch began to refine the windmill, eventually implementing thousands for various applications such as irrigation, land drainage, grain-grinding, saw-milling and the processing of commodities.
With the current awareness of global warming and the human impact upon the environment, there is an increasing shift towards greener, ecologically-friendly technologies. While fossil fuel-fired and nuclear powerplants have been standard methods of power generation for the last century, alternative methods for power generation, particularly from renewable energy sources such as the sun and wind have been attracting increasing attention from industry, governments and the general public.
Modern windmills for power generation are growing in popularity, with wind farms being established in many countries around the world. Modern windmills come in a variety of sizes and configurations, but many associate windmills with the large horizontal wind turbines used for large scale energy generation. These large turbines can stand as tall as 90 meters, with generally three equidistantly spaced blades measuring upwards of 30 meters each. More recently, however, there is growing interest for smaller turbine units that are better suited to farm and residential application.
On most horizontal wind turbines, there is a control that slows down or completely stops the rotation of the wind blades during higher than anticipated wind velocity.
The traditional “wheel vane” windmill that was used primarily for pumping water, and still in operation today, is a classic example of rotating the body of the windmill oblique to the wind to attain a complete stoppage of the “wheel vane”. The foregoing cut-off system, located at the top of the windmill, consists of a centrifugal set up of weights such that when its rotation is increased, the weights expand outward and strikes a lever that releases the spring loaded wind vane. The wind vane then rotates parallel to the “wheel vane” which stops the windmill rotation completely. It is necessary to manually reload the centrifugal weight system so that the wind vane is again at right angles to the “wheel vane”. The windmill does not automatically reset into an operating configuration.
The modern brake system for reducing rotational velocity can consist of either a “disk” or “drum” assemblage or an “generator/alternator” reverse technology. The “disk” or “drum” assemblage can be activated remotely by a wired or wireless mechanism. However, there is greater wear on the brake pads if the wind blades remain at right angles to the wind, resisting the braking mechanism. The “generator/alternator” reverse technology is automatically applied when the torque on the wind blades is exceeded. With this technology, the rotor rotating inside the stator of the alternator has the ability to act as a brake.
Both braking systems may be used simultaneously, rotating the body of the wind turbine oblique to the wind, and when rotation is decreased, using the “disk” or “drum” brakes to completely stop the rotation of the wind blades. There is no existing mechanism whose sole purpose is to slow down the wind blades, without complete stoppage.
With smaller wind turbines that are constructed for residential or farm use, it is preferable to use a simpler braking mechanism than those described above.